How will the BBC report the results of the US election? This guide explains where the results come from, what exit polls are, and how states are called.

What is the source for the BBC's election results?

This year, the BBC is reporting state calls made by the ABC news network - these are projections of which candidate has won that state's electoral college votes.

When a state call is made by ABC, our results desk in Washington will update the BBC's electoral college vote tally for each candidate.

All other election data, including popular votes and Congressional results, is provided by the Associated Press (AP).

The BBC receives this information from an electronic feed and uses it to compile running totals of popular votes state by state and nationwide.

AP is the sole organisation responsible for providing results for the major American media networks. The information they provide will form the basis for election results, but different broadcasters may decide to interpret partial results in different ways.

How do the results take shape and what are "projected results"?

Initially, the outcome of the US election is likely to be a projection, based on exit polls and/or partial results. The result will be clearly labelled as "projected" until all the votes are counted.

The reason for this is that states are often called, or declared, for a candidate, on the basis of incomplete figures. The American electoral system enables each state to release partial results to the public well before they have counted every vote. Results are later confirmed once all the votes have been counted.

For races that are not very close, ABC, along with other US networks, are likely to project a winner as soon as the polls close, based on exit poll data. For closer races, the news networks will wait until there is more actual vote data. It can take hours or even all night.

If a projection is not immediate, it does not mean it is too close to call, rather it may simply be too early to call because the networks have insufficient data.

Are the projections ever wrong?

Yes, particularly if the election is very close. Most memorably the major US networks, including Fox, CNN, NBC, CBS, and ABC, said Al Gore would win Florida in 2000, only to retract that and then say George W Bush won it, and then to retract that as the result was under dispute. The presidency eventually went to Mr Bush.

What is an exit poll?

Exit polls are polls of voters, gathered after they have voted. They are used in two main ways.

They can help predict the outcome of an election before all the votes are counted, and they may also provide information on demographics. For example, they could show which candidate appealed most to women voters, or who got the most support from the Hispanic community.

This year, exit polls are being handled solely by Edison Media Research and Mitofsky International.

The BBC does not have access to the detailed exit poll data.

Is Washington DC a state?

No. DC, or the District of Columbia, is not a state, but it does receive three electoral college votes. DC is able to vote for the president but it does not have senators or congressmen of its own.